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Opqdonut's Haskell Exercises

Note! You probably want to check out my Haskell MOOC (course page, GitHub) instead! It's completely free and open and is based on these exercises, but also contains study material and other improvements. These exercises still work, but this repository isn't maintained.

Quick Start

If these instructions don't work for you, see the instructions for using cabal instead of stack

1. Install Stack

2. Download dependencies by running

    $ stack build
   

3. Then check you can actually run the tests with:

    $ stack runhaskell W0Test.hs
   

   This should print Everything seems to be OK!. If you see any errors, you might not have a problem with your Haskell installation.

4. Generate the exercise templates (files W*.hs):

    $ make
   

5. Now you can edit W1.hs and see how well you did by running

    $ stack runhaskell W1Test.hs
   

6. You can also play around with your solutions interactively by running

    $ stack ghci W1.hs
   

Introduction

This is a collection of small and simple Haskell exercises with unit tests. This means your answers to the exercises are checked by the computer – making these exercises great for self-study.

The exercises don't really include any reading material, so you should study some Haskell tutorial, e.g. Learn You A Haskell For Great Good! while working on the exercises.

If bump into an exercise that talks about terms you don't understand, look them up in a tutorial or google them! The exercises are meant to encourage you to learn, not check that you already know stuff :)

I created this set of exercises for a Haskell course I held at Helsinki University because I couldn't find a set of good Haskell exercises anywhere. I hope somebody else finds them useful as well.

Contents

The exercises are split into sets called "weeks", each containing about 20 exercises. You are meant to work through the weeks in order, but you don't need to get every exercise in a week right to move on.

The topics of the weeks are

• W1: basics, syntax, defining functions, pattern matching, recursion
• W2: lists, strings, higher-order functions, polymorphism
• W3: data types
• W4: IO
• W5: type classes
• W6: Monads
• W7: recap of weeks 1-6

Working on the Excercises

• Read and edit the Wn.hs files according to the instructions

• Don't remove or change any type signatures (things like foo :: String -> String) that are already in the files

• Check your answers for week n with stack runhaskell WnTest.hs (or alternatively cabal exec runhaskell WnTest.hs if you're not using stack)

• A typical test failure looks like this:

    Testing 11
    *** Failed! Falsifiable (after 1 test):
    0
    0
    Expected 1, got 3
    FAIL
  

  This means that the function from exercise 11 failed the test when the two arguments were 0 and 0. The result should have been 1, but it was 3.

  I'm sorry if the test failures aren't always understandable :/

• You can also play around with your solutions interactively by running stack ghci Wn.hs (or cabal exec ghci Wn.hs). This is a good idea for instance when you don't understand the test failures.

Solutions

This repository also contains solutions to the exercises. You can get the solutions for week n by running

$ make WnSol.hs

The solutions are also visibile under the directory templ/. Don't look there if you don't want spoilers!